Archive

Most embedded software practitioners – sadly, not all – know that some form of what is normally called “Mutual Exclusion” is necessary when a read-write resource is shared among two or more concurrent activities, particularly (but not necessarily only) when test-and-set operations are involved. The expression “Mutual Exclusion” is so entrenched as a generic concept that I feel obliged to use it as such, but sometimes it is anything but mutual. Read more…

When it comes to interrupts, SKC++’s guiding principle is “minimum interference”.

Some kernels require that interrupts be processed internally, the internal Interrupt Service Routine (ISR) calling out to an ordinary user function, sometimes also called an ISR, confusingly. Some others let you code the ISR yourself but impose restrictions on how you do it.

SKC++ does not require you to alter the way you program ISRs; Read more…

Although I separated the ideas of posting an untrammelled event, using post, and sending a message (which also posts an event), using send, this is not such a good idea for receiving messages. One of the key things about an SKC++ task is that it should be able to wait at a single point in its processing in order to get something to process and that it should deal with only one event or message at a time. Accordingly, the wait function has been enhanced to deal with message reception, as well as with raw events. Read more…

This is a relatively short article, as the sending of messages from one task to another is straightforward. I decided to defer its counterpart, “Receiving Messages”, until next time because there are several things to consider there, making the subject worthy of an article of its own. Read more…

Local Message-Passing

Message-passing is used, in an RTOS-based system, to provide a safe way of transferring data from one context to another or, in other words, from task to task. What is safe, though, is not always efficient and vice versa. Read more…